1. Field of the Invention
This application relates broadly to improvements in automatic backwash filtering systems. More particularly, it concerns improved underdrain filter plate installations in such systems.
2. Description of the Prior Art
Automatic backwash filter systems (ABFS) as known in the art are exemplified in U.S. Pat. Nos. 3,239,061; 4,133,766; 4,617,131; 4,764,288 and 5,089,130 currently assigned to Infilco Degremont Inc., the assignee of the invention disclosed herein. The disclosures of these patents are incorporated herein by reference.
In the known automatic backwash filter systems, horizontal underdrain filter plates are typically held in place against upward movement by angle pieces which are fastened by their vertical webs to the cell sheet and with the horizontal web holding down the top surface of the filter plate. During installation of such arrangements, caulking is applied on an lateral ledge of the cell sheet, the filter plate is laid in this chaulking, additional chaulking is applied to the top edge of the underdrain plate and the retaining angle piece is then bolted to the cell sheet. The angle pieces present limited bearing surface against the underdrain plates requiring particular care with the installation and holding of the distance between cell sheets to relatively tight tolerances.
The present invention addresses problems associated with the known arraignments for mounting of underdrain filter plates in position relative to cell sheets in automatic backwash filter systems and provides improved cell sheet structures that simplify cell sheet and filter plate installation, provide firmer retention for filter plates and reduce assembly costs.